Monitor and keyboard not recognizing each oth

Hello,
I cannot get me monitor and keyboard and mouse to recognize each other. On the monitor, there is kinda orange light that comes on, then, the light will go green just for a minute, a message will come up on the monitor saying it is in power save mode, hit any key on keyboard, then when I do hit a key, the light goes off on the monitor, and doesn't recognize anything. I can't get anything on the computer. what can I do ?